Synthesis of maleic anhydride

ABSTRACT

Maleic anhydride is produced by the oxidation of 1,3-butadiene, n-butylenes, crotonaldehyde and furan with molecular oxygen in the vapor phase in the presence of catalytic oxides of antimony, molybdenum, at least one element selected from the group consisting of niobium, zirconium, titanium and tantalum and optionally a reducing agent capable of reducing at least part of the molybdenum in the catalyst to a valence state below +6 selected from the group consisting of hydrazine hydrate, molybdenum, tungsten, magnesium, aluminum, and nickel. This catalyst may optionally contain one or more elements selected from the group consisting of Li, Ag, Ce, Cd, Co, As, Si, Zn, Ge, Bi, Ru, Pt, U, Al and Ni. Especially desirable yields of maleic anhydride are obtained from 1,3-butadiene in the presence of a catalyst wherein molybdenum metal is used as a reducing agent.

BACKGROUND OF THE INVENTION

Generally, in the commercial production of maleic anhydride by thecatalytic oxidation of hydrocarbons, it is of ultimate importance to usecatalysts which give high conversions of hydrocarbons to maleicanhydride.

Maleic anhydride is conventionally prepared by the oxidation of benzene;however, high percentages of converted benzene are lost in the form ofcarbon oxides. This process create unnecessary waste in that two carbonatoms are oxidized to useless waste.

The oxidation of 1,3-butadiene to produce maleic anhydride eliminatesthis waste. This process has been conducted before in the art usingvarious catalysts, for example West German Pat. No. 1099111 disclosesthe preparation of maleic anhydride by the catalytic vapor phaseoxidation of 4-carbon hydrocarbons in the presence of catalysts of thecomposition AO₃ --B₂ O₅ --M₂ O₅ --N_(x) O--R₂ O (in which A is Cr, Mo,W, or U; B is V or Nb; M is P, As, Sb or Bi; N is Cu, Ag, Fe, Co or Ni;R is Li, Na, K, Cs or Rb; x is 1- 2). U.S. Pat. No. 3,907,834 disclosesthe preparation of maleic anhydride from n-butylenes, 1,3-butadiene,crotonaldehyde and furan in the presence of a catalyst containingantimony, molybdenum, and a reducing agent selected from the groupconsisting of molybdenum, tungsten, magnesium, aluminum and nickel.British Pat. No. 1,157,117 discloses the production of maleic anhydridefrom a saturated aliphatic hydrocarbon having 4 carbon atoms in themolecule or an unsaturated aliphatic hydrocarbon having 4 or 5 atoms inthe molecule in the presence of a catalyst comprising an oxide ofmolybdenum and at least one other oxide if tin, antimony, titanium, ironor tungsten.

The primary object of the present invention is to provide a process forproducing maleic anhydride using novel catalysts with improved yields ofmaleic anhydride and decreased waste byproducts.

It is a further object of this invention to provide a method for makingthe novel and improved catalyst of the character indicated.

SUMMARY OF THE INVENTION

In accordance with the present invention has been discovered a processfor the preparation of maleic anhydride comprising contacting a mixtureof an unsaturated organic compound selected from the group consisting ofn-butylenes, 1,3-butadiene, crotonaldehyde and furan and anoxygen-containing gas with a catalyst at a temperature in the range offrom about 250° C. to 600° C., under a pressure of from about 1 to 500psi, and wherein the molar ratio of oxygen to the organic compound is inthe range of from 2:1 to 40:1, the improvement comprising:

using as the catalyst a catalyst of the formula

    A.sub.a E.sub.c Mo.sub.e Sb.sub.f O.sub.x

wherein A is at least one element selected from the group consisting ofniobium, zirconium, titanium and tantalum;

E is a member selected from the group consisting of hydrazine hydrate, afinely divided metal of molybdenum, tungsten, magnesium, aluminum, ornickel;

and wherein a is a number from 0.01 to 6;

c is a number from 0 to 0.2;

e and f are numbers from 1 to 9 ;

x is a number which satisfies the valence requirements of the otherelements present;

and wherein at least some of the molybdenum in the catalyst ismaintained at a valence state below +6;

said catalyst optionally containing one or more elements selected fromthe group consisting of lithium, silver, cerium, cadmium, cobalt nickel,arsenic, silicon, zinc, germanium, bismuth, ruthenium, platinum anduranium.

Maximum results are achieved when the starting material is1,3-butadiene. Improved results are obtained when the basicantimony-molybdenum catalyst is promoted with single elements oftantalum, zirconium, titanium or niobium but, from the standpoint ofoptimum benefits and catalyst effectiveness, it is preferred that acombination of titanium and niobium or titanium and zirconium beincorporated in the catalyst to enhance the activity of the basiccatalyst system.

As noted, the catalyst employed in the present invention may be anycatalyst delineated by the above formula, however, preferred catalystsare represented by the formula

    A.sub.a D.sub.b E.sub.c Ti.sub.d Mo.sub.e Sb.sub.f O.sub.x

wherein A is at least one element selected from the group consisting ofniobium, zirconium, and tantalum;

D is at least one element selected from the group consisting of cadmium,cobalt, arsenic, nickel, lithium and cerium;

E is a member selected from the group consisting of hydrazine hydrate, afinely divided metal of molybdenum, tungsten, magnesium, aluminum ornickel;

wherein a and d are numbers from 0 to 3;

b is a number from 0 to 1;

c is a number from 0 to 0.2;

a + d is not zero;

e and f are numbers from 1 to 9;

x is a number which satisfies the valence requirements of the otherelements present;

and wherein at least some of the molybdenum in the catalyst ismaintained at a valence state below +6.

Excellent results are achieved using catalysts wherein D is at least oneelement selected from the group consisting of arsenic, lithium andcerium. Catalysts of particular interest are described wherein a and dare numbers from 0.01 to 3 or wherein b is 0 to 0.5. Especiallydesirable results are observed using catalysts wherein a and d arenumbers from 0.01 to 1.0 and b is zero.

Also preferred in the invention are those catalysts wherein E is addedto the catalyst as molybdenum metal. After the catalyst is prepared,this metal may be at least partially present in the form of an oxide oroxide complex. The catalysts which are prepared using molybdenum metalare preferably those wherein c is 0.001 to 0.2 and e and f are numbersfrom 1.0 to 8.0.

The method used for preparing the catalyst of this invention is criticalto the process for producing maleic anhydride. The method employeddeparts from the classical procedures involving coprecipitation orimpregnation techniques and preferably involves contacting the compoundcontaining hexavalent molybdenum with a controlled amount of a reducingagent. By the preferred procedure of the invention a compound containinghexavalent molybdenum, preferably molybdenum trioxide, ammoniumheptamolybdate or mixture thereof, in an aqueous suspension isprereduced in a controlled manner so that at least some of themolybdenum is reduced to a valence state below +6 before the compoundcontaining hexavalent molybdenum is mixed with the antimony trioxide.For example, a mixture of molybdenum trioxide and ammoniumheptamolybdate may be contacted with a given amount of molybdenum metalpowder to effect a certain and reproducible degree of reduction. A widerange of reducing agents can be employed to effect the desiredreduction. Representative examples of strong reducing agents includefinely divided or colloidal metals of molybdenum, tungsten, magnesium,aluminum or nickel and hydrazine hydrate. Representative examples ofweak reducing agents are lower valent antimony oxides and salts andother metal oxides or salts containing metals in their lower oxidationstates. When powdered metals are employed, the amount of metal reactedranges from 0.01 to 0.2 atom per mole of the hexavalent molybdenumpresent.

One method of preparing the catalyst involves refluxing an aqueousslurry of antimony trioxide, molybdenum trioxide and/or ammoniumheptamolybdate and compounds containing the respective promoter elementsfor a period of one-half hour to 16 hours. The amount of water presentin solution can range from 500 to 2000 mls. per mole of the molybdenumpresent. During this period the slurry darkens. Water is removed fromthe slurry by evaporation until a thick homogenous material is obtainedwhich on drying at 110°-130° C. overnight emerges as a dark blue-greenor blue-gray solid. It is hypothesized that the darker color whichdevelops in the catalyst is the result of the reduction of molybdenum,at least in part, to a lower oxidation state in the oxidation reductionreaction occurring between hexavalent molybdenum and trivalent antimony.

Although preferably the compound containing hexavalent molybdenum isprereduced before reaction with antimony trioxide, beneficial resultsare achieved by reacting the compound containing hexavalent molybdenumwith antimony trioxide followed by reaction with the reducing agent, orby reacting the three components together followed by the addition ofcompounds containing the respective promoter elements.

The catalyst may be activated by calcining it in air at a temperature ofabout 350° C. to 700° C. for a period of up to five hours or more. Bythe preferred procedure of the invention, the catalyst is not calcinedprior to being reacted with the desired hydrocarbon. The hydrocarbonreacted may be n-butylenes, 1,3-butadiene, crotonaldehyde, furan or amixture thereof. Preferred is the use of 1,3-butadiene or a mixture ofhydrocarbons that are produced in refinery streams. The molecular oxygenis most conveniently added as air, but synthetic streams containingmolecular oxygen are also suitable. In addition to the hydrocarbon andmolecular oxygen, other gases may be added to the reactant feed. Forexample, steam or nitrogen could be added to the reactants.

The ratio of the reactants may vary widely and are not critical. Theratio of the hydrocarbon to molecular oxygen may range from about 2 toabout 30 moles of oxygen per mole of hydrocarbon. Preferred oxygenratios are about 4 to about 20 moles per mole of hydrocarbon.

The reaction temperature may vary widely and is dependent upon theparticular hydrocarbon and catalyst employed. Normally, temperatures ofabout 250° C. to about 600° C. are employed with temperatures of 325° C.to 480° C. being preferred.

The catalyst may be used alone or a support could be employed. Suitablesupports include silica, alumina, clay, Alundum, silicon carbide, boronphosphate, zirconia, titania, thoria, diatomaceous earth, and aluminumphosphate. The catalysts are conveniently used in a fixed-bed reactorusing tablets pellets or the like or in a fluid-bed reactor using acatalyst preferably having a particle size of less than about 300microns. The contact time may be as low as a fraction of a second or ashigh as 50 seconds. The reaction may be conducted at atmospheric,superatmospheric or subatmospheric pressure.

Excellent results are obtained using a coated catalyst consistingessentially of an inert support material having a diameter of at least20 microns and an outer surface and a continuous coating of said activecatalyst on said inert support strongly adhering to the outer surface ofsaid support.

By use of these coated catalysts in the reaction to produce maleicanhydride, a very low exotherm is realized allowing for better controlof the reaction. High single pass yields are exhibited and theelimination of undesirable byproducts is obtained.

The special coated catalyst consists of an inner support material havingan outside surface and a coating of the active catalytic material onthis outside surface. These catalysts can be prepared by a number ofdifferent methods.

The support material for the catalyst forms the inner core of thecatalyst. This is an essentially inert support and may havesubstantially any particle size, although a diameter of greater than 20microns is preferred. Especially preferred in the present invention foruse in a commercial reactor are those supports which are spherical andwhich have a diameter of about 0.2 cm. to about 2 cm. Suitable examplesof essentially inert support materials include: Alundum, silica,alumina, alumina-silica, silicon carbide, titania and zirconia.Especially preferred among these supports are Alundum, silica, aluminaand aluminasilica.

The catalysts may contain essentially any proportions of support andcatalytically active material. The limits of this relationship are onlyset by the relative ability of the catalyst and support material toaccommodate each other. Preferred catalysts contain about 10 to about100 percent by weight of catalytically active material based on theweight of the support.

The preparation of these coated catatlysts can be accomplished byvarious techniques. The basic method of preparing these catalysts is topartially wet the support material with a liquid. The support should notbe wet on the outside surface of the total mass. It should appear to bedry to the touch. If the support is wet, then the active catalyticmaterial may agglomerate into separate aggregates when coating of thesupport is attempted. These partially wet supports are then contactedwith a powder of the catalytically active material and the mixture isgently agitated until the catalyst is formed. The gentle agitation ismost conveniently conducted by placing the partially wet support in arotating drum or jar and adding the active catalytic material. This isvery economically done.

Using the catalysts of the invention in the preparation of maleicanhydride, excellent yields are obtained in a convenient reaction withlow amounts of byproducts.

SPECIFIC EMBODIMENTS Comparative Examples A to F and Examples 1 to 43

Preparation of Maleic Anhydride Using Catalysts Containing Promoters ofInvention Compared with Use of Base Catalyst.

A 20 cc. fixed-bed reactor was constructed of a 1.3 cm. inside diameterstainless steel tubing equipped with a full length 0.3 cm. axialthermowell. Catalysts prepared as described below were charged to thereactor and heated to the reaction temperature and 1,3-butadiene wasreacted with air in the proportions specified in TABLES I to V at anapparent contact time of 3 to 4 seconds. The total usable acids wererecovered and analyzed. Maleic anhydride was determined bypotentiometric titration.

Comparative Example A and Examples 1 to 10

The catalysts were prepared as follows:

Comparative Example A SbMo₃ O_(x) + Mo° ₀.06

A slurry was prepared consisting of 72.0 grams of molybdenum trioxide(Baker green), 0.96 grams of molybdenum metal powder (Sylvania) and 1000mls. of distilled water. This aqueous slurry was refluxed for two hoursfollowed by the addition of 24.27 grams of antimony trioxide; theresulting mixture was refluxed an additional hour, evaporated to a thickpaste, dried overnight at 110° C. to 130° C. and ground and screened to20-30 mesh.

EXAMPLES 1 TO 39 -- REACTION OF 1,3-BUTADIENE USING VARIOUS CATALYSTS OFTHE INVENTION EXAMPLES 1 TO 10

Catalysts of the invention were employed to prepare maleic anhydridefrom 1,3-butadiene in the same manner shown in Comparative Example A.The catalysts for these experiments were prepared as follows:

EXAMPLE 1 SbMo₃ Ti₀.6 O_(x) + Mo°₀.06

A slurry was prepared consisting of 72.0 grams of molybdenum trioxide,0.96 grams of molybdenum metal powder, 7.98 grams of pigment gradetitanium dioxide (Dupont) and 1000 mls. of distilled water. This aqueousslurry was refluxed for two hours followed by the addition of 24.27grams of antimony trioxide; the resulting mixture was refluxed anadditional hour, evaporated to a thick paste, dried overnight at110°-130° C., and ground and screened to 20-30 mesh.

EXAMPLES 2 AND 3

Catalysts of the formulae SbMo₃ Ti₀.3 O_(x) + Mo°₀.06 and SbMo₃ Ti₁.2O_(x) + Mo°₀.06 were prepared in the same manner described in Example 1using 3.99 grams of anatase titanium dioxide or 15.96 grams of anatasetitanium dioxide, respectively.

EXAMPLES 4 TO 6

In the same manner described in Example 1, catalysts of the formulaeSbMo₃ Nb₀.6 O_(x) + Mo°₀.06, SbMo₃ Ta₀.6 O_(x) + Mo°₀.06 and SbMo₃ Zr₀.6O_(x) + Mo°₀.06 were prepared by replacing the titanium dioxide with13.32 grams of niobium pentoxide, 22.2 grams of tantalum pentoxide, or12.3 grams of zirconium dioxide, respectively.

EXAMPLE 7 Part A. SbMo₃ Ti₀.6 Nb₀.1 O_(x) + Mo°₀.06

A slurry was pepared consisting of 72.0 grams of molybdenum trioxide,0.96 grams of molybdenum metal powder, 7.98 grams of high surface areatitanium dioxide, 2.22 grams of niobium pentoxide and 1000 mls. ofdistilled water. This aqueous slurry was refluxed for two hours followedby the addition of 24.27 grams of antimony trioxide; the resultingmixture was refluxed an additional hour, evaporated to a thick paste,dried over the weekend at 110° C., and ground and screened to 20-30 meshsize.

Part B. 33%(SbMo₃ Ti₀.6 Nb 0.1O_(x) + Mo°₀.06) + 66 2/3% Alundum

A catalyst was prepared in the same manner described in Part A, exceptthe dry catalytic particles were ground and screened to less than 50mesh size and coated on 10-30 mesh SA 5209 Alundum balls by taking 40grams of Alundum, partially wetting the Alundum with 3.6 grams of waterand adding 20 grams of active catalyst prepared above in 5 equalportions. During and after each addition, the Alundum was rolled in aglass jar. The powder was evenly coated onto the surface of the Alundumand the final product was dried. A hard uniform coated catalyst wasobtained that consisted of the Alundum support with the continuous,strongly adhering coating of the active catalyst. The catalyst was thendried in an oven at 110°-130° C. for 16 hours.

EXAMPLES 8 TO 10

In the same manner described in Example 7, Part A, catalysts of theformulae SbMo₃ Ti₀.6 Zr₀.1 O_(x) + Mo°₀.06, SbMo₃ Ti₀.6 As₀.1 O_(x) +Mo°₀.06, and SbMo₃ Ti₀.6 Ce₀.1 O_(x) + Mo°₀.06 were prepared byreplacing the niobium pentoxide with 2.05 grams of zirconium dioxide (ZrCorp. of America), 1.65 grams of arsenous trioxide, or 2.87 grams ofcerium dioxide, respectively.

Comparative Examples B and C and Examples 11 to 37

The results of the experiments in the oxidation of 1,3-butadiene toproduce maleic anhydride are shown in TABLES I to IV below. The resultsare stated in terms of per pass conversion which is defined as ##EQU1##

In the same manner described above, catalysts of the invention may beeffectively utilized in the oxidation of furan, n-butylenes andcrotonaldehyde.

                                      TABLE I                                     __________________________________________________________________________    Performance of Catalysts of the Invention Compared with                       Base Sb-Mo Catalyst in the Preparation of Maleic Anhydride                                      Temp° C.                                                                     Molar Feed Ratio                                                                       Per Pass Conversion, %                       Example                                                                            Catalyst     Bath                                                                             Bed                                                                              Air/BD   Total Acid                                                                            MAA                                  __________________________________________________________________________    Comp. B                                                                            SbMo.sub.3 O.sub.x + Mo.sup.o 0.06                                                         369                                                                              383                                                                              25.12    68.79   63.93                                Comp. C                                                                            SbMo.sub.3 O.sub.x + Mo.sup.o 0.06                                                         387                                                                              407                                                                              25.51    66.82   61.13                                11   SbMo.sub.3 Ti.sub.0.3 O.sub.x + Mo.sup.o 0.06                                              371                                                                              389                                                                              27.28    73.61   70.91                                12   SbMo.sub.3 Ti.sub.0.6 O.sub.x + Mo.sup.o 0.06                                              371                                                                              381                                                                              26.39    73.45   70.09                                13   SbMo.sub.3 Ti.sub.0.6 O.sub.x + Mo.sup.o 0.06                                              399                                                                              413                                                                              26.55    75.10   71.45                                14   SbMo.sub.3 Ti.sub.1.2 O.sub.x + Mo.sup.o 0.06                                              372                                                                              385                                                                              27.02    74.34   71.07                                15   SbMo.sub.3 Nb.sub.0.6 O.sub.x + Mo.sup.o 0.06                                              371                                                                              390                                                                              27.69    74.86   71.74                                16   SbMo.sub.3 Ta.sub.0.6 O.sub.x + Mo.sup.o 0.06                                              373                                                                              389                                                                              27.09    78.70   74.60                                17   SbMo.sub.3 Zr.sub.0.6 O.sub.x + Mo.sup.o 0.06                                              372                                                                              385                                                                              29.49    76.64   72.61                                __________________________________________________________________________

                                      TABLE II                                    __________________________________________________________________________    Preparation of Maleic Anhydride from 1,3-Butadiene                            Using the Catalyst SbMo.sub.3 Ti.sub.0.6 Zr.sub.0.1 O.sub.x + Mo.sup.o        0.06                                                                          Temp° C.                                                                          Molar Feed Ratio                                                                       Per Pass Conversion, %                                    Example                                                                            Bath                                                                             Bed                                                                              Air/BD   Total Acid                                                                            MAA Hours on Stream                               __________________________________________________________________________    18   396                                                                              404                                                                              29.60    75.50   72.25                                                                             17.5                                          19   406                                                                              417                                                                              30.22    75.07   72.29                                                                             18.1                                          20   396                                                                              404                                                                              32.71    80.82   78.06                                                                             134.2                                         21   387                                                                              31.80                                                                            81.08    77.98   136.8                                             22   381                                                                              391                                                                              32.26    76.43   74.49                                                                             138.5                                         __________________________________________________________________________

                                      TABLE III                                   __________________________________________________________________________    Preparation of Maleic Anhydride from 1,3-Butadiene                            Using the Catalyst SbMo.sub.3 Ti.sub.0.6 Nb.sub.0.1 O.sub.x                   + Mo.sup.o.sub.0.06                                                           Temp° C.                                                                          Molar Feed Ratio                                                                       Per Pass Conversion, %                                    Example                                                                            Bath                                                                             Bed                                                                              Air/BD   Total Acid                                                                            MAA Hours on Stream                               __________________________________________________________________________    23   385                                                                              396                                                                              31.34    76.48   73.21                                                                             17.8                                          24   386                                                                              395                                                                              27.71    75.23   72.36                                                                             20.3                                          25   392                                                                              404                                                                              30.21    76.69   73.48                                                                             22.0                                          26   392                                                                              403                                                                              32.05    81.52   78.0                                                                              38.5                                          27   400                                                                              416                                                                              31.19    78.0    75.73                                                                             40.8                                          28   392                                                                              409                                                                              30.40    78.18   75.93                                                                             43.8                                          29   388                                                                              400                                                                              31.58    80.57   77.85                                                                             60                                             30* 387                                                                              394                                                                              84.72    80.81   78.61                                                                             63.7                                          31   387                                                                              406                                                                              22.12    74.61   70.57                                                                             65.4                                          32   384                                                                              399                                                                              33.03    80.08   75.67                                                                             131.5                                         __________________________________________________________________________     *1.24 seconds contact time                                               

                                      TABLE IV                                    __________________________________________________________________________    Preparation of Maleic Anhydride from 1,3-Butadiene                            Various Catalysts of the Invention                                                                Temp° C.                                                                     Molar Feed Ratio                                                                       Per Pass Conversion, %                     Example                                                                            Catalyst       Bath                                                                             Bed                                                                              Air/BD   Total Acid                                                                            MAA                                __________________________________________________________________________    33   SbMo.sub.3 Ti.sub.0.6 Nb.sub.0.1 O.sub.x + Mo.sup.o 0.06                                     402                                                                              406                                                                              37.22    79.41   76.38                                   (coated)                                                                 34   SbMo.sub.3 Ti.sub.0.1 Nb.sub.0.1 O.sub.x + Mo.sup.o 0.06                                     412                                                                              416                                                                              36.88    77.73   75.11                                   (coated)                                                                 35   SbMo.sub.3 Ti.sub.0.6 As.sub.0.1 O.sub.x + Mo.sup.o 0.06                                     412                                                                              426                                                                              28.61    78.37   74.90                              36   SbMo.sub.3 Ti.sub.0.6 As.sub.0.1 O.sub.x + Mo.sup.o 0.06                                     410                                                                              419                                                                              72.48    75.37   72.58                              37   SbMo.sub.3 Ti.sub.0.6 Ce.sub.0.1 O.sub.x + Mo.sup.o 0.06                                     385                                                                              404                                                                              28.2     75.33   73.17                              __________________________________________________________________________

EXAMPLES 38 TO 43

The catalysts SbMo₃ Ti₀.6 Nb₀.1 O_(x) + Mo°₀.06 and SbMo₃ Ti₀.6 Zr₀.1O_(x) + Mo°₀.06 were prepared using a mixture of molybdenum trioxide andammonium heptamolybdate. The experimental results showing the oxidationof 1,3-butadiene in the presence of these catalysts appear in TABLE V.

These catalysts were prepared as follows:

EXAMPLE 38 SbMo₃ Ti₀.6 Nb₀.1 O_(x) + Mo°₀.06

A slurry was pepared consisting of 54.0 grams of molybdenum trioxide,22.07 grams of ammonium heptamolybdate, 0.96 grams of molybdenum metalpowder, 7.98 grams of pigment grade titanium dioxide, 2.22 grams ofniobium pentoxide and 1000 mls. of distilled water. This aqueous slurrywas refluxed for two hours followed by the addition of 24.27 grams ofantimony trioxide; the resulting mixture was refluxed an additionalhour, evaporated to a thick paste, dried over the weekend at 110° C.,and ground and screened to 20-30 mesh size.

EXAMPLE 39

In the same manner described in Example 38, a catalyst of the formulaSbMo₃ Ti₀.6 Zr₀.1 O_(x) + Mo°₀.06 was prepared by replacing the niobiumpentoxide with 2.05 grams of zirconium dioxide.

                                      TABLE V                                     __________________________________________________________________________    Effect of Using a Mixture of Molybdenum Trioxide                              And Ammonium Heptamolybdate in the Preparation of Catalysts of the            Invention                                                                                         Temp° C.                                                                     Molar Feed Ratio                                                                       Per Pass Conversion, %                     Example                                                                            Catalyst       Bath                                                                             Bed                                                                              Air/BD   Total Acid                                                                            MMA Hours on                       __________________________________________________________________________                                                   Stream                         40   SbMo.sub.3 Ti.sub.0.6 Nb.sub.0.1 O.sub.x + Mo.sup.o.sub.0.06                                 360                                                                              371                                                                              30.04    78.86   74.67                                                                             23                             41   SbMo.sub.3 Ti.sub.0.6 Nb.sub.0.1 O.sub.x + Mo.sup.o.sub.0.06                                 372                                                                              382                                                                              30.53    82.12   77.98                                                                             21.6                           42   SbMo.sub.3 Ti.sub.0.6 Zr.sub.0.1 O.sub.x + Mo.sup.o.sub.0.06                                 371                                                                              388                                                                              34.8     80.23   76.3                                                                              286                            43   SbMo.sub.3 Ti.sub.0.6 Zr.sub.0.1 O.sub.x + Mo.sup.                                           385ub.0.06                                                                       403                                                                              35.4     83.35   78.7                                                                              407.8                          __________________________________________________________________________

We claim:
 1. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 psi, and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    A.sub.a E.sub.c Mo.sub.e Sb.sub.f O.sub.x

wherein A is titanium in combination with at least one of niobium, zirconium and tantalum; E is a member selected from the group consisting of hydrazine hydrate, a finely divided metal of molybdenum, tungsten, magnesium, aluminum, or nickel; and wherein a is a number from 0.01 to 6.0; c is a number from 0 to 0.2; e and f are numbers from 1 to 9; x is a number which satisfies the valence requirements of the other elements present; and wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6;said catalyst optionally containing one or more elements selected from the group consisting of lithium, silver, cerium, cadmium, cobalt nickel, arsenic, silicon, zinc, germanium, bismuth, ruthenium, platinum and uranium.
 2. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 psi, and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    A.sub.a D.sub.b E.sub.c Ti.sub.d Mo.sub.e Sb.sub.f O.sub.x

wherein A is at least one element selected from the group consisting of niobium, zirconium, and tantalum; D is at least one element selected from the group consisting of cadmium, cobalt, arsenic, nickel, lithium and cerium; E is a member selected from the group consisting of hydrazine hydrate, a finely divided metal of molybdenum, tungsten, magnesium, aluminum or nickel; wherein a and d are positive numbers less than or equal to 3; b is a number from 0 to 1; c is a number from 0 to 0.2; e and f are numbers from 1 to 9; x is a number which satisfies the valence requirements of the other elements present; and wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6.
 3. The process of claim 2 wherein 1,3-butadiene is reacted.
 4. The process of claim 2 wherein b is 0 to 0.5.
 5. The process of claim 2 wherein the temperature is 325° to 480° C.
 6. The process of claim 2 wherein E is added to the catalyst as molybdenum metal.
 7. The process of claim 6 wherein c is 0.001 to 0.2 and e and f are numbers from 1.0 to 8.0.
 8. The process of claim 2 wherein a mixture of molybdenum trioxide and ammonium heptamolybdate is employed in the preparation of the catalyst.
 9. The process of claim 2 wherein the catalyst is prepared by refluxing an aqueous mixture of ammonium heptamolybdate, molybdenum trioxide and a reducing agent.
 10. The process of claim 2, wherein a and d are numbers from 0 to 1.2.
 11. The process of claim 2 wherein D is at least one element selected from the group consisting of arsenic, lithium and cerium.
 12. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 psi, and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    A.sub.a E.sub.c Mo.sub.e Sb.sub.f O.sub.x

wherein A is at least one element selected from the group consisting of niobium, tantalum and zirconium; E is a member selected from the group consisting of hydrazine hydrate, a finely divided metal of molybdenum, tungsten, magnesium, aluminum or nickel; and wherein a is a number from 0.01 to 6; c is a number from 0 to 0.2; e and f are numbers from 1 to 9; x is a number which satisfies the valence requirements of the other elements present; and wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6;said catalyst optionally containing one or more elements selected from the group consisting of lithium, silver, cerium, cadmium, cobalt nickel, arsenic, silicon, zinc, germanium, bismuth, ruthenium, platinum and uranium.
 13. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 psi, and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    A.sub.a E.sub.c Mo.sub.e Sb.sub.f O.sub.x

wherein A is tatanium and zirconium; E is a member selected from the group consisting of hydrazine hydrate, a finely divided metal of molybdenum, tungsten, magnesium, aluminum or nickel; and wherein a is a number from 0.01 to 6; c is a number from 0 to 0.2; e and f are numbers from 1 to 9; x is a number which satisfies the valence requirements of the other elements present; and wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6;said catalyst optionally containing one or more elements selected from the group consisting of lithium, silver, cerium, cadmium, cobalt nickel, aresenic, silicon, zinc, germanium, bismuth, ruthenium, platinum, and uranium.
 14. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 psi, and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    Nb.sub.a D.sub.b E.sub.c Ti.sub.d Mo.sub.e Sb.sub.f O.sub.x

wherein D is at least one element selected from the group consisting of cadmium, cobalt, arsenic, nickel, lithium and cerium; E is a member selected from the group consisting of hydrazine hydrate, a finely divided metal of molybdenum, tungsten, magnesium, aluminum or nickel; wherein a and d are positive numbers less than or equal to 3; b is a number from 0 to 1; c is a number from 0 to 0.2; e and f are numbers from 1 to 9; x is a number which satisfies the valence requirements of the other elements present; and wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6.
 15. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 psi, and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    Ta.sub.a D.sub.b E.sub.c Ti.sub.d Mo.sub.e Sb.sub.f O.sub.x

wherein D is at least one element selected from the group consisting of cadmium, cobalt, arsenic, nickel, lithium and cerium; E is a member selected from the group consisting of hydrazine hydrate, a finely divided metal of molybdenum, tungsten, magnesium, aluminum or nickel; wherein a and d are positive numbers less than or equal to 3; b is a number from 0 to 1; c is a number from 0 to 0.2; e and f are numbers from 1 to 9; x is the number which satisfies the valence requirements of the other elements present; and wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6.
 16. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 psi, and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    Zr.sub.a D.sub.b E.sub.c Ti.sub.d Mo.sub.e Sb.sub.f O.sub.x

wherein D is at least one element selected from the nickel, lithium and cerium; E is a member selected from the group consisting of hydrazine hydrate, a finely divided metal of molybdenum, tungsten, magnesium, aluminum or nickel; wherein a and d are positive numbers less than or equal to 3; b is a number from 0 to 1; c is the number from 0 to 0.2; a + d is not zero; e and f are numbers from 1 to 9; x is a number which satisfies the valence requirements of the other elements present; and wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6.
 17. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 psi, and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    A.sub.a E.sub.c Mo.sub.e Sb.sub.f O.sub.x

wherein A is titanium and niobium; E is a member selected from the group consisting of hydrazine hydrate, a finely divided metal of molybdenum, tungsten, magnesium, aluminum or nickel; and wherein a is a number from 0.01 to 6; c is a number from 0 to 0.2; e anf f are numbers from 1 to 9; x is a number which satisfies the valence requirements of the other elements present; and wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6;said catalyst optionally containing one or more elements selected from the group consisting of lithium, silver, cerium, cadmium, cobaltnickel, arsenic, silicon, zinc, germanium, bismuth, ruthenium, platinum, and uranium.
 18. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 psi, and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    A.sub.a E.sub.c Ti.sub.d Mo.sub.e Sb.sub.f O.sub.x

wherein A is at least one element selected from the group consisting of niobium, zirconium, and tatalum; E is at least one element selected from the group consisting of hydrazine hydrate, a finely divided metal of molybdenum, tungsten, magnesium, aluminum or nickel; wherein a and d are numbers from 0.01 to 3; c is a number from 0 to 0.2; e and f are numbers from 1 to 9; x is a number which satisfies the valence requirements of the other elements present; and wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6.
 19. The process of claim 18 wherein a mixture of molybdenum trioxide and ammonium heptamolybdate is employed in the preparation of the catalyst.
 20. The process of claim 18 wherein the catalyst is prepared by refluxing an aqueous mixture of ammonium heptamolybdate, molybdenum trioxide, and a reducing agent.
 21. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 p.s.i., and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    A.sub.a E.sub.c Mo.sub.e Sb.sub.f O.sub.x

wherein A is at least one element selected from the group consisting of niobium, zirconium, titanium and tantalum; E is a member selected from the group consisting of hydrazine hydrate, a finely divided metal of molybdenum, tungsten, magnesium, aluminum, or nickel; and wherein a is a number from 0.01 to 6; c is a number from 0 to 0.2; e and f are numbers from 1 to 9; x is a number which satisfies the valence requirements of the other elements present; wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6;and wherein said catalyst contains at least one element selected from the group consisting of cadmium, cobalt, arsenic, lithium and cerium.
 22. The process of claim 21 wherein E is added to the catalyst as molybdenum metal or hydrazine hydrate.
 23. The process of claim 21 wherein A is titanium.
 24. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 p.s.i., and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    A.sub.a D.sub.b E.sub.c Ti.sub.d Mo.sub.e Sb.sub.f O.sub.x

wherein A is at least one element selected from the group consisting of niobium, zirconium, and tantalum; D is at least one element selected from the group consisting of cadmium, cobalt, arsenic, nickel, lithium, and cerium; E is a member selected from the group consisting of hydrazine hydrate, a finely divided metal of molybdenum, tungsten, magnesium, aluminum, or nickel; wherein a and d are numbers from 0.01 to 3; b is a number from 0 to 1; c is a number from 0 to 0.2; e and f are numbers from 1 to 9; x is a number which satisfies the valence requirements of the other elements present; and wherein at last some of the molybdenum in the catalyst is maintained at a valence state below +6.
 25. The process of claim 24 wherein 1,3-butadiene is reacted.
 26. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° to 600° C., under a pressure of from about 1 to 500 p.s.i., and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    Zr.sub.a D.sub.b E.sub.c Ti.sub.d Mo.sub.e Sb.sub.f O.sub.x

wherein Z is one element selected from the group consisting of cadmium, cobalt, arsenic, nickel, lithium and cerium; E is molybdenum metal; wherein a and d are positive numbers equal to or less than 3; b is a number from 0 to 1; c is a number from 0..001 to 0.2; e and f are numbers from 1.0 to 8.0; x is a number which satisfies the valence requirements of the other elements present; and wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6.
 27. The process of claim 26 wherein the catalyst is SbMo₃ Ti₀.6 Zr₀.1 O_(x) +Mo°₀.06.
 28. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 p.s.i., and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    Nb.sub.a D.sub.b E.sub.c Ti.sub.d Mo.sub.e Sb.sub.f O.sub.x

wherein D is one element selected from the group consisting of cadmium, cobalt, arsenic, nickel, lithium and cerium; E is molybdenum metal; wherein a and d are positive numbers equal to or less than 3; b is a number from 0 to 1; c is a number from 0.001 to 0.2; e and f are numbers from 1.0 to 8.0; x is a number which satisfies the valence requirements of the other elements present;and wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6.
 29. The process of claim 28 wherein the catalyst is SbMo₃ Ti₀.6 Nb₀.1 O_(x) +Mo°₀.06.
 30. A process for the preparation of maleic anhydride comprising contacting a mixture of an unsaturated organic compound selected from the group consisting of n-butylenes, 1,3-butadiene, crotonaldehyde and furan and an oxygen-containing gas with a catalyst at a temperature in the range of from about 250° C. to 600° C., under a pressure of from about 1 to 500 p.s.i., and wherein the molar ratio of oxygen to the organic compound is in the range of from 2:1 to 40:1, the improvement comprising:using as the catalyst a catalyst of the formula

    A.sub.a E.sub.c Ti.sub.d Mo.sub.e Sb.sub.f O.sub.x

wherein A is at least one element selected from the group consisting of niobium, zirconium and tantalum; E is a member selected from the group consisting of hydrazine hydrate, a finely divided metal of molybdenum, tungsten, magnesium, aluminum or nickel; and wherein a and d are numbers from 0.01 to 1.0; c is a number from 0 to 0.2; e and f are numbers from 1 to 9; x is a number which satisfies the valence requirements of the other elements present;and wherein at least some of the molybdenum in the catalyst is maintained at a valence state below +6. 